The present invention is an oil spill detector which is intended to monitor a limited area around it. The unit is designed to be mounted on a buoy or on a seawall and to detect the presence of fresh oil spills that are in the channel marked by the buoy or seawall. Solid state sensors are the preferred sensing devices for this type of detector because of their simplicity and reliability; they have no moving parts whose operation could be disrupted either by the corrosive atmosphere or by the motion of the sea if buoy mounted.
The sensors used in the present invention are made by Figaro Engineering Inc. of Osaka, Japan and are known as Taguchi Gas Sensors, or TGS sensors, model 812. The TGS model 812 sensor is a heated semiconductor chip which increases its conductivity when certain organic vapors are absorbed on its surface. The principal active ingredient in the semiconductor chip is stannic oxide, which is heated by a resistance heater incorporated into the chip. Heating minimizes the sensitivity of the chip to water vapor and at the same time speeds the reversal of the adsorption process so that the sensor quickly recovers after its exposure to organic vapors. The sensors require a heater voltage of 5.0+0.2 volts and a circuit voltage of 10-15 volts.
Uncovered TGS sensors have one drawback to being used as oil spill detectors: they are sensitive to airborne gaseous contaminants such as the carbon monoxide in engine exhaust as well as hydrocarbon vapors. An uncovered sensor would thus respond to a passing ship just as it would to an oil spill. Attempts to find a membrane that would pass crude oil vapors but not carbon monoxide were unsuccessful; hence the present invention was devised to overcome the problem.
Accordingly, it is an object of the present invention to provide a hydrocarbon vapor detector unit that is insensitive to carbon monoxide.
It is a further object to provide a unit of the above type which uses solid state devices as sensors.
It is a further object to provide a unit of the above type which can be mounted either on a buoy or seawall.